重构会话管理功能，由后端 opencode 发放 sessionId，后端做 scope

tests/conversations/store.test.ts

@@ -0,0 +1,64 @@
+import { afterEach, beforeEach, describe, expect, it } from "bun:test";
+import { mkdtemp, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+import { ConversationStore } from "../../src/conversations/store.js";
+
+describe("ConversationStore", () => {
+  let tempDir: string;
+  let store: ConversationStore;
+
+  beforeEach(async () => {
+    tempDir = await mkdtemp(join(tmpdir(), "tjwater-conversation-"));
+    store = new ConversationStore(tempDir);
+    await store.initialize();
+  });
+
+  afterEach(async () => {
+    await rm(tempDir, { force: true, recursive: true });
+  });
+
+  it("issues backend-managed session ids when absent", async () => {
+    const { record, created } = await store.ensure({
+      actorKey: "actor-1",
+      projectId: "project-1",
+      projectKey: "project-key-1",
+      userId: "user-1",
+    });
+
+    expect(created).toBe(true);
+    expect(record.sessionId).toStartWith("chat-");
+    expect(record.ownerUserId).toBe("user-1");
+    expect(record.status).toBe("active");
+  });
+
+  it("touches metadata and preserves scoped ownership", async () => {
+    const { record } = await store.ensure({
+      actorKey: "actor-2",
+      projectId: "project-2",
+      projectKey: "project-key-2",
+      sessionId: "existing-session",
+      userId: "user-2",
+    });
+
+    const touched = await store.touch(record, {
+      title: "新标题",
+    });
+
+    expect(touched.title).toBe("新标题");
+    expect(touched.updatedAt >= record.updatedAt).toBe(true);
+
+    const fetched = await store.get(
+      {
+        actorKey: "actor-2",
+        projectId: "project-2",
+        projectKey: "project-key-2",
+        userId: "user-2",
+      },
+      "existing-session",
+    );
+    expect(fetched?.sessionScopeKey).toBe(record.sessionScopeKey);
+    expect(fetched?.title).toBe("新标题");
+  });
+});